Six short lines on the head of a capscrew indicate a hardness of?

Six short lines on the head of a capscrew indicate a hardness of?

• A. Grade 2
• B. Grade 5
• C. Grade 12.9
• D. Grade 8

Answer: (D)

Markings on a bolt head communicate its strength class, so you can quickly judge how much load it’s designed to handle. Six short lines across the head are the visual code for a high-strength cap screw—specifically SAE Grade 8. This class uses a tougher alloy and is chosen for connections that must resist heavy forces, which is why it’s indicated by that many lines. Weaker classes show fewer lines or none at all, and the marking system for metric bolts uses numeric codes rather than row patterns of lines.

Markings on a bolt head communicate its strength class, so you can quickly judge how much load it’s designed to handle. Six short lines across the head are the visual code for a high-strength cap screw—specifically SAE Grade 8. This class uses a tougher alloy and is chosen for connections that must resist heavy forces, which is why it’s indicated by that many lines. Weaker classes show fewer lines or none at all, and the marking system for metric bolts uses numeric codes rather than row patterns of lines.